good question! the answer is NO. The tetracyclin kills good and bad bacteria. it is the 'bad' bacteria that causes acne, not the good, good bacteria actually helps acne. so you will only be helping yourself by taking probiotics, your tetra will still work just as well, an you'll be getting some good bacteria too.. just make sure you dont take them at the same time.. take the probiotics 2 hours before or after the anti's.. so the anti wont totally kill the probiotic... hope that helps! caroline